The invention relates to axial piston pumps having oblique disks. One known type of axial piston pump has a piston drum that is rotatably displaceable by way of a rotatable drive shaft and that has a number of bore holes disposed therein.
Pistons are disposed in the piston bore holes and are displaceable between a lower dead-center point and an upper dead-center point. The pistons are each driven by an articulated piston rod that is reciprocably displaceable by way of an oblique disk. The disk is adjustable in its inclination with respect to the piston drum. A holder is provided to guide the piston rods. The holder is always oriented in parallel with respect to the oblique disk. The drive shaft is supported by way of a ball-type formation in a central receiving bore of the holder.
An axial piston pump with the aforementioned features is known from Delivery Catalog 2500 D of Parker Hannifin GmbH, Hydraulic Controls Division, 41564 Kaarst, 3rd edition (1997), page 1-64. The drive shaft, which rotationally displaces the piston drum via a toothed engagement, and which itself is driven, is supported by way of its forward, ball-type end on the central receiving bore of a holder. The holder is adjustable by way of the oblique disk and, in that connection, is always oriented in parallel to the oblique disk. The piston rods that connect to the pistons extend through the holder in corresponding bore holes. The end of each piston is coupled to a travel shoe that, during rotation of the piston drum relative to the fixed oblique disk, will run along the oblique disk so that the piston rods are displaced reciprocally, and thereby drive the pistons. The holder holds the travel shoes (that run along the oblique disk when the piston drum rotates) in place on the oblique disk with a predetermined bias and rotates synchronously with the piston drum.
In known axial piston pumps, as long as the driving of the piston drum takes place by way of the drive shaft coupled with it in form-fit fashion, a torque will be transferred from the piston drum through the pistons that reciprocate in the piston bore holes and the piston rods that extend through the holder. One disadvantage of this structure is that, for pistons resting in the lower dead-center point in the piston bore hole, a minimal axial covering of the piston must be provided by the wall of the piston bore hole in order to guarantee an adequate transfer of torque between the piston drum and the piston. When the piston is in that position, the angle of engagement of the oblique disk is limited, which limits the output of the axial piston pump.
With oblique disk pumps known in the art, the maximum angle of engagement, as a rule, is about 18 degrees. If the output of the pump is increased by way of a greater angle of engagement of the oblique disk, this will necessarily lead to the structural size of the piston drum being increased in the axial direction since, in addition to the longer piston travel achieved with a greater angle of engagement, one will need to account for the necessary minimal covering of the piston with the piston bore hole. With a zero-degree angle of engagement of the oblique disk with respect to the drive shaft, the extension of the piston rods through the holder must correspond exactly to the piston bore holes in the piston drum because of the task of transmitting torque to the holder that is accorded the pistons. An increase in the angle of engagement will lead to an undesirable increase in the structural size of the pump in the radial direction, since otherwise the travel shoes would displace too closely to the drive shaft.
The object of the invention is thus to improve upon an axial piston pump, that has the features mentioned above, in such a way that the angle of engagement of the oblique disk can be made greater without changing the structural size of the pump.
The solution to this objective encompasses advantageous developments and modifications associated with the invention in accordance with the content of the claims appended to this specification.